Abstract: A leaky coaxial cable includes an inner conductor member extending in axis direction, to propagate signal; an insulator member covering the inner conductor member; a first outer conductor member having conductor wires on circumference surface of the insulator member with shielding density so as to leak a part of the signal to outside thereof; and a plurality of second outer conductor members contacting the first outer conductor member and arranged with constant pitch in the axis direction, to shield the signal; wherein, in the axis direction, each electrical length of the second outer conductor members is the same as electrical length between adjacent second outer conductor members; and the pitch is in range of 1/(1+0.766?) times to 3/(1+?) times of propagation wavelength of the signal in the inner conductor member, where ? is wavelength shortening coefficient of the propagation wavelength to free-space wavelength of the signal.